In the field of internal combustion engines for automobiles, a variety of variable valve mechanisms have conventionally been proposed, with changeable lift characteristic amounts such as the intake/exhaust valve lift amount, operation angle, and valve timing. Additional background on variable valve timing is described in Unexamined Japanese Patent Application Publication No. 2002-54466 and in U.S. Pat. No. 6,843,226, titled “Intake control apparatus for internal combustion engine,” issued on Jan. 18, 2005, both of which are commonly assigned.
Feedback control is preferably performed based on the detected value of lift characteristic amounts to maintain lift characteristic amounts at their target values with good precision. As described in said Unexamined Japanese Patent Application Publication No. 2002-54466, such feedback control technology is commonly known. Simply explained, target values for the lift characteristic amounts are calculated according to the engine operating conditions (load, number of revolutions, etc.), detection values equivalent to the actual lift characteristic amount values are obtained using an appropriate sensor, and the command value for the variable valve mechanism actuator is calculated based on the deviation of these target values and detection values.
However, if feedback control is continued during a sensor error when the detection values cannot be accurately obtained due to sensor failure or error, the actual lift characteristic amount can be vastly different from the target value, and the risk of losing engine operability occurs. Therefore, in said Unexamined Japanese Patent Application Publication No. 2002-54466, when a sensor error occurs, the system switches to an open control toward the maximum or minimum side of the variable range for the lift characteristic amounts.